Esomeprazole is a proton pump inhibitor (brand names Nexium; Lucen; Esopral and Axagon in Italy) developed and marketed by AstraZeneca which is used in the treatment of dyspepsia, peptic ulcer disease (PUD), gastroesophageal reflux disease (GORD/GERD) and Zollinger-Ellison syndrome. Esomeprazole is the S-enantiomer of omeprazole (marketed as Losec/Prilosec), and AstraZeneca claims improved efficacy of this single enantiomer product over the racemic mixture of omeprazole. However, this alleged greater efficacy has been disputed, with many claiming it offers no benefit from its older form. (see below). Esomeprazole was the third biggest selling pharmaceutical drug in the world for 2005, bringing in 5.7 billion dollar sales for the year of 2005.